1. Field of the Invention
The present invention generally relates to an apparatus and method for eye examination. In particular, the invention relates to a method and apparatus for ophthalmoscopically projecting a stimulus test target onto a portion of the retina of an eye so as to create a test target. The position of the test target may be determined and recorded using a spectral perimetry system. The invention also permits spectral sensitivity measurement using collected electroretinogram (ERG) data and allows this data to be recorded and stored.
2. Description of the Prior Art
A number of methods and devices are known for examining the retina of a human eye. Often these methods and devices involve imaging devices. One such device is described in U.S. Pat. No. 4,676,612 issued to Wada et at. Wada et al. describes an apparatus comprising a target projecting system for projecting onto a retina a target image to be measured; a focalizing means, such as a TV monitor, for detecting the focus of the target to be measured and for focalizing it on the retina; an optical transfer function measuring system for detecting and measuring the contrast of the target image to be measured. The apparatus may further comprise means for comparing the measured optical transfer function with that of a normal eye and means for rotating the target image around an optical axis.
U.S. Pat. No. 4,279,478 issued to Matsumura also discloses an eye examining instrument for examination of the retina. Matsumura's apparatus uses a fixation object for maintaining the direction of the eye's line of vision, and a bright test object movable in a plane conjugate with the fundus of the eye with respect to an observation optical system. The eye fundus image is guided to an image pickup tube and displayed on a Braun tube. Recording paper and a marker cooperating with the test object are also provided for memorizing the position of the test object each time the examination is completed. Images of the marks recorded on the recording paper are superimposed on the eye fundus image, observed, and photographed.
U.S. Pat. No. 4,991,953 issued to Pflibsen et al. describes a scanning laser vitreous camera for imaging the vitreous of an eye. The apparatus features an imaging instrument wherein optics define first and second symmetrically placed windows in the iris through which a slit illumination and an observation beam synchronously scan a region of the vitreous. In a preferred embodiment, the observation and illumination paths are alternately interchanged to produce a pair of stereo images formed along identical optical paths. Alternately, a common scanning element illuminates the vitreous, which is viewed along symmetrical left and right observation imaging paths.
Physicians have recorded ERG responses to a number of different stimuli. A pattern onset-offset technique has been used which employs color-contrast patterns composed of elements discriminable only by hue but not by brightness or saturation. See 28 M. Korth et al., Luminance-Contrast Evoked Responses and Color-Contrast Evoked Responses in the Human Electroretinogram, Vision Res. 41 (1988).
An earlier version of Korth's work studied the transitions between pattern and luminance-related responses. See M. Korth, E.R.G. Responses to Patterned Light Stimuli, (1983). There Korth produced pattern onset-offset stimuli using a projected target beam split into two parallel paths and recombined into a single beam. While the beam is split, a shutter along one path is opened or closed to increase or decrease the light content along that path in association with pattern onset and offset resulting from the degree of vibration of the pattern.
Color flash stimulation has also been used to generate ERG data and has been reported in S. Mills & H. Sperling, Red/green Opponency in the Rhesus Macaque ERG Spectral Sensitivity is reduced by Bicuculline, Visual Neuroscience 217 (1990).
Other work has employed pattern reversal stimulation to evoke ERG responses using temporal alternations of a 500 nm checkerboard stimulus pattern superimposed on a uniform monochromatic field of experimentally variable wavelength. S. Wu & J. Armington, Isolation of Scotopic Human Electroretinograms Using Color Adaptation and Pattern Reversal Stimuli, Vision Res. 1277 (1989).
There is known in the art a hand held ophthalmoscope which projects flash ERG stimuli. This stimulator is rumored to have been modified to also incorporate pattern ERG, but not yet successfully. This device has no features for perimetry or spectral sensitivity determination.
The above described systems, while useful, do not permit a physician to examine smaller areas within specific retinal locations and to use Maxwellian view optics to stimulate the small areas at high radiance levels in order to obtain large. ERG signal amplitudes for analyses. Further, these systems do not permit measurement of spectral sensitivity at different positions on and at different afferent stages of the retina.